Evaluation of overall extraction constants for the crown ether-complex ions of alkali and alkaline-earth metal with counter picrate ions from water into nitrobenzene based on their component equilibrium constants

Abstract

Extraction constants (Kex±) for complex ions (MLz+) of L=15-crown-5 ether (15C5), benzo-15C5, 18-crown-6 ether (18C6), benzo-18C6, dibenzo-18C6, or dibenzo-24-crown-8 ether (DB24C8) with A−=picrate ion (Pic−) into nitrobenzene (NB) were evaluated at z=1 and 2. Here, the following thermodynamic relation was used for their evaluation: Kex±=[MLz+]NB([A−]NB)z/([Mz+][L]NB[A−]z)=KD,M(KD,A)zβ1NB; KD, j and β1NB denote an individual distribution constant of species j (=Mz+, A−) into the NB phases and a stability constant for MLz+ in the phases. Using these results and the number of water (w) molecules co-extracted with M+, L, and ML+ into the NB phases, an effect of the w molecules released with the ML+ formation in the NB phases on Kex± was discussed. The above results were also applied for the prediction of an actual separation of Ba2+ from Sr2+ or Ca2+, using DB24C8 or 18C6 as L, Pic− as A−, and NB as diluent. Then, it was predicted that DB24C8 is more effective as L for the separation of Ba2+ from Ca2+ than 18C6. No effective L for the separation of Cs+ from Na+ was found out, using A−=I− and NB as the diluent.